1. Field of the Invention
The present invention relates to an ink-jet recording device, an image-processing device, and an image processing method, and in particular relates to a decimation process of adjacent dots of black ink and color ink in the event of performing recording using black ink and color ink.
2. Description of the Related Art
Printers serving as an information output device of a personal computer, word processor, facsimile apparatus, or the like for example, which perform recording of information such as desired characters or images to a sheet-type recording medium such as a paper sheet or film or the like, are widely used. Various methods are known as recording methods of a printer, but the ink-jet method has attracted attention recently for reasons such as capability of non-contact recording onto a recording medium such as a paper sheet or the like, ease of coloring, extremely quiet operations, and so forth.
For an ink-jet method configuration, a serial-recording-method is generally used, whereby recording is performed by alternately performing recording scanning, which moves a carriage, whereupon a recording head is mounted, back and forth in the main scanning direction, and a conveying operation for conveying the recording medium in the sub scanning direction which intersects with the main scanning direction. During movement of the carriage, an image is formed by discharging ink from a recording head according to desired recording information. Note that by discharging multiple colors of ink from the recording head, color images are formed.
An ink-jet recording device which can easily form color images can also be used for many monochrome recording such as documents. In the case of such monochrome recording, realizing sharpness of the recorded image (characters or lines), clearness, and a high recording density (dark black) is required. A technique is known whereby the permeability of the black ink as to the recording medium is lowered (permeability is lowered) and the color material of the black ink is suppressed from permeating into the recording medium, in order to realize sharpness, clearness, and a high recording density of the recording image.
On the other hand, when a color image is recorded with an ink-jet recording device, a phenomenon can occur wherein, as different colors of ink are imparted on the recording medium adjacent to one another, the inks can mix with one another at the border portions thereof (also called feathering or border bleeding). When bleeding occurs at the border portions of the different color inks, the recording quality of the color image is decreased. In order to decrease the occurrence of this bleeding and form high-quality images, permeability of the color inks as to a recording medium is increased (permeability is improved), and prevents the color inks from mixing on a surface which is a non-recording medium.
However, in the case of using a black ink with low permeability, and color ink with high permeability, the two problems described below may occur.
First, since the color ink with high permeability permeates the recording medium, fixing time (the time until the ink is dry) is fast, but the color material within the ink of the black ink with low permeability does not easily permeate the recording medium, and so the fixing time is long. Therefore, in the case of continuously recording onto a recording medium, i.e. in the case of forming images onto multiple sheets of a recording medium and continuously discharging these, before the black ink imparted on the previous page completely dries, the image forming of the following page can be ended and discharged. Consequently, the surface on the previous page whereupon an image is formed (recording face) and the back face of the surface on the following page whereupon an image is formed (back face of the recording medium) rub together and soil the back face of the following recording medium page. Further, the recording face of the previous page is also soiled, and image quality is lowered. Such soiling of the recording face and back face of the recording medium is called “smearing”. This smearing increases markedly as the time required for recording becomes shorter due to increases in recording speed of the recording device.
Also, with a recording device which records onto a long recording medium (paper roll), the recording medium is cut with a cutter after image forming, and the recording medium having been subjected to cutting is discharged into a receiving basket which is provided on the floor or on the recording device. At this time, the recording medium having been subjected to recording is not dry, and therefore with a recording device performing recording onto a long recording medium, even in the case of forming an image onto one recording medium sheet, the floor or basket into which the recording medium is discharged, or further the recording face also can become soiled.
Secondly, at a border region wherein the black ink and color ink have each been imparted on the recording medium, feathering of the black ink and color ink (border bleeding) can occur. This border bleeding occurs because the low permeability black ink remains on the recording medium but when the high permeability color ink imparted in an adjacent region permeates the recording medium, the black ink also permeates together. By bleeding occurring at the border of the black ink and the color ink, the image quality is reduced significantly.
As solutions for the above two problems, first through third measures are taken.
The first solution is a method for using fixing means of ink which enables the fixing of ink with heat or wind. According to the technology disclosed in Japanese Patent Laid-Open No. 07-047762, by using a fixing means, the ink is fixed quickly to the recording medium, and so smearing and border bleeding can be suppressed.
However, with this first solution, an increased device size and increased cost cannot be avoided in order to provide the fixing means. Also, with a serial-recording-method recording device, the transporting operation of the recording medium (medium subjected to recording) is performed continuously, and so when performing fixing of the ink at the fixing means, unevenness can occur in the sending process.
The second solution is a method for controlling discharge standby of the recording medium, so that discharge of the following page is not performed until the ink of the previously discharged page is dry. By temporarily stopping the recording operation to the following page until the ink of the previously discharged page is sufficiently dry, or by temporarily stopping the discharge operation of the recording medium after having an image formed on the following page, the occurrence of smearing can be suppressed.
However, with this second solution, the recording operation or the discharge operation is stopped until the ink on the previous page is dry, and therefore results in decrease of throughput, and the time required for recording becomes longer.
The third solution is a method for imparting the high permeability color ink so as to be layered over the black ink in a low-permeability-black-ink-imparting region. By discharging color ink layered over the black ink in a black ink imparting region, when the color ink permeates the recording medium the black ink also permeates together and the fixing of the black ink is accelerated, thus decreasing the occurrence of smearing. Further, a technology is disclosed in Japanese Patent Laid-Open No. 2003-159827, wherein an ink setting of the type is used whereby black ink and color ink are mixed together to react and coagulate, thus suppressing border bleeding. By performing the third solution or the method described in Japanese Patent Laid-Open No. 2003-159827, smearing and border bleeding can be suppressed without increasing the size of the device or decreasing throughput.
However, with the third solution, the black ink permeates the recording medium together with the color ink which is discharged in the black ink imparting region, and the color ink can bleed to the outer side of the black ink recording region. Consequently, the sharpness of the black image is deteriorated, and recording quality of black characters deteriorates. That is to say, sharpness, clearness, and high recording density of the recorded image cannot be realized.
Therefore, with the Japanese Patent Laid-Open No. 2005-144795, a method is thought of for decreasing the occurrence of smearing and border bleeding, while suppressing the decrease of recording quality of the black characters or the like. This Japanese Patent Laid-Open No. 2005-144795 detects a non-edge portion of the black dots formed with the black ink and a recording region wherein black ink and color ink is adjacent, and imparts color dots on the black-dot non-edge portion and the black ink coloring region on the recording medium wherein color and black inks are adjacent to one another. Further, a reduction technology is described in Japanese Patent Laid-Open No. 2005-144795 to reduce the discharge amount of the black dots on the black-dot non-edge portion. Thus, sharpness of black images such as characters, lines, and figures with sharp angles can be maintained, while improving on smearing and fixing, as well as decreasing border bleeding.
An example wherein sharpness of black images such as characters is maintained, and smearing and fixing are improved with the technology described in Japanese Patent Laid-Open No. 2005-144795, is shown in FIGS. 4C and 4D. FIG. 4C shows character data recorded with black ink, and FIG. 4D is an example of recording, having changed the density reduction of black ink and imparting conditions of the color ink at the edge portion and the non-edge portion. Thus, outlines are clear, and characters (and lines) can be formed with sharp images.
However, with the technology described in the above-described Japanese Patent Laid-Open No. 2005-144795, the following problems could occur.
FIG. 4A is an image showing the region wherein black ink is discharged. Also, FIG. 4B is an image showing the region wherein the technology described in the above-described Japanese Patent Laid-Open No. 2005-144795 is used to discharge black ink and color ink. With the technology described in the above-described Japanese Patent Laid-Open No. 2005-144795, the periphery (several dots worth) of the region of the image where black ink is not discharged (the blank pixels in the diagram) is determined to be the edge portion of a region wherein black ink is discharged, and also is not adjacent to the region wherein color ink is imparted. Therefore, reducing process of the black ink or imparting of the color ink is not performed. The blank pixels in the diagram are not a region for discharging color ink, and therefore this edge portion is determined to not be adjacent to a region wherein color ink is imparted, and so the imparting of color ink is not performed. On the other hand, a region separated from a region not including black ink by a predetermined number or more of dots (the region in the upper left in FIG. 4A, and so forth) is determined to be a non-edge portion of a region including black ink. Therefore, in order to reduce smearing, the discharge data of black ink is reduced to lessen the amount of black ink imparted, and also color ink is imparted, and the results in FIG. 4B are obtained. Note that FIG. 4B is an example of results wherein, at a non-edge portion of FIG. 4A, the black ink is reduced by 50%, and color dots are imparted at the ratio of cyan 5.5%, magenta 2.9%, and yellow 2.6%.
As is clear from FIG. 4B, the density and hue of the color changes between the edge portions and non-edge portions of the black ink, and further it is apparent that the gradation of the image markedly declines. With the technology in Japanese Patent Laid-Open No. 2005-144795 shown in FIGS. 4A through 4D, the black images of characters or lines which are not adjacent to the region of color ink have a clean and sharp outline, but with a picture image, sharpness can be deteriorated and image quality can decrease.